I. Field of the Invention
This invention relates to a process for preparing water soluble and water swellable highly substituted polysaccharide derivatives. More specifically, it relates to a general process for preparing polysaccharide derivatives under controlled conditions such that the derivative is produced efficiently and at high substitution and is readily isolated in solid form.
II. Brief Description of the Prior Art
Method for preparing water soluble or water swellable derivatives of polysaccharides such as starches, cellulose and gums are well known in the literature. (See, for example, R. L. Whistler, Methods in Carbohydrate Chemistry, Vol. IV, 1964, pgs. 279-311; R. L. Whistler, et al., Starch - Chemistry and Technology, Vol. II, 1967, pgs. 293-430; and R. L. Davidson and N. Sittig, Water-Soluble Resins, 2nd Ed., 1968, Chapter 2). Such methods generally involve the use of high dilution aqueous techniques, dry reactions, reactions conducted in water-solvent mixtures or aqueous inorganic salt systems.
Most of the techniques of the prior art are limited in a practical sense because of the high solution viscosities associated with these types of highly substituted natural polymers. Since the water solubility of the polysaccharide increases, for example, as the number of derivatizing groups introduced is increased, there is a limit to the degree of substitution that can be reached by prior art techniques involving water, water-salt or water-solvent systems. Dry reactions are usually run at elevated temperatures and as such may be accompanied by some degradation of the polysaccharide backbone. Additional problems with the prior art techniques are encountered in recovering the derivatized polysaccharide as a solid product.
It is therefore an object of the present invention to provide a simple and efficient process for preparing water soluble and water swellable polysaccharide derivatives.
It is also an object of the invention to provide such a process wherein the derivatization may be carried out in aqueous environments at high concentrations while avoiding the problems of the prior art aqueous techniques.
Finally, it is an object to provide a process for the production of such derivatives which can be isolated directly from the reaction mixture in the form of solid beads.